The invention relates to an internal combustion engine provided with means for preventing overspeeding of the engine, said means including an exhaust brake associated with the engine.
An exhaust brake is sometimes used to supplement the wheel brakes of a very heavy vehicle when descending a steep gradient, to prevent any tendency for the vehicle to run away causing overspeeding of the engine and consequential damage thereto, for example to its valve mechanism. An exhaust brake is well known per se and comprises a valve operable to obstruct the escape of exhaust gases when the vehicle is in gear and overdriving, that is to say when the wheels are transmitting drive back to the engine. The engine is thus caused to absorb torque by functioning as a compressor.
If a very heavy vehicle does run away, the driver is suddenly required to perform a number of different operations. These include steering the safest possible course, applying the wheel brakes, almost or entirely cutting off the supply of fuel to the engine, changing into a low gear ratio, and applying the exhaust brake where one is fitted. It is difficult to carry out all these operations quickly and effectively under emergency conditions.
It has been proposed to actuate an exhaust brake automatically by electro-hydraulic means controlled by a continuously monitored engine parameter or by electrical means controlled simultaneously by two such parameters, but these proposals have been complex and therefore costly and prone to malfunction.
The object of the present invention is to provide inexpensive but reliable means for actuating an exhaust brake automatically and thus easing the task of the driver if the vehicle runs away.